English: Francis Everitt, Principal Investigator for the Gravity Probe B Mission at Stanford University, makes a point during a press conference, Wednesday, May 4, 2011, to discuss NASA's Gravity Probe B (GP-B) mission which has confirmed two key predictions derived from Albert Einstein's general theory of relativity, which the spacecraft was designed to test at NASA Headquarters in Washington. The experiment, launched in 2004, used four ultra-precise gyroscopes to measure the hypothesized geodetic effect, the warping of space and time around a gravitational body, and frame-dragging, the amount a spinning object pulls space and time with it as it rotates. Photo Credit: (NASA/Paul E. Alers)